The present invention relates to electrochromic devices for varying the transmittance or reflection to light, such as windows for buildings, transportation (e.g., motor vehicles, buses, trains, planes, boats). Devices from this invention may also be used for displays (including indicators), and rear-view mirrors for vehicles, motor cycles, etc.
Reversibly variable electrochromic devices are known in the art. In such devices, the intensity of light (e.g., visible, infrared, ultraviolet or other distinct or overlapping electromagnetic radiation) is modulated by passing the light through an electrochromic medium. The electrochromic medium is disposed between two conductive electrodes, at least one of which is typically transparent, and causes the medium to undergo reversible electrochemical reactions when potential differences are applied across them. The electrochromic devices may be divided in two distinct types. In one, a stack of thin films is used on a single substrate that comprises of all the transparent conductors, electrolyte and other electrode layers. Examples of these devices are in US patent applications 2007/0097481 and 2007/0103761. In the other type of EC devices two substrates are used, which have pre-deposited layers of conductors and may also have other pre-deposited redox electrode layers in addition to the conductors. These substrates are put together as a sandwich where the center is a liquid or a polymeric solid electrolyte. Examples are described in U.S. Pat. Nos. 3,280,701; 4,712,879; 4,902,108; 5,007,718; 6,178,034 and 6,266,177. Electrochromic materials in this invention are those that change color when oxidized or reduced.
For EC windows it is desired that the devices have good memory, this means once the window is colored or bleached, it remains in that optical state for a long period of time with minimum or no power, i.e., their power consumption is low to keep the desired optical state or one may be able to power the device intermittently without changing the transmission too much from the desired value. Such devices, with good memory, usually employ additional electrochromic and/or ion storage coatings on the substrates which are laminated with an ion conducting (or an electrolyte) layer as described in U.S. Pat. Nos. 6,266,177; 6,172,794 and US patent application 2006/0159610. In these devices, the added processing operations related to additional coatings deposition, their etching and reduction of at least one layer (if used) adds to the cost.
Devices with a sequence of thin coatings on a single substrate are also expensive to produce, particularly with increasing area. First, such all thin film stacks are sensitive to yield due to defects in thin coatings and, second, the deposition of layers by physical vapor deposition (PVD) is expensive as many of these layers are thick and are typically in the range of 300 to 1000 nm. Further, many of these devices need additional layers to reduce shorting and may also require additional processing steps for ion intercalation (e.g., see US patent application 2007/0097481).
To reduce cost of EC devices it is desirable to produce components using mass scale production methods. One method is to use a lamination process. This is a standard method where a polymeric sheet is laminated to a substrate. This method is well understood and is widely available. For example, laminated glass is available in a price range acceptable to end-customers for use in scatter (or shatter) resistant glass in climates where large wind loads are expected, and in automotive industry these windows reduce outside noise, and in case of windshields all cars in U.S. are required to only use laminated glass by the Federal Motor Vehicle Safety Standards. One way of implementing this procedure to manufacture EC devices cost effectively is to produce a solid laminating film with all the EC characteristics using mass processes such as extrusion and casting. The conductive substrates are being produced in large sizes and volumes for many other applications which may be used for these devices.
Glass with transparent conductive coatings, for example, fluorine doped tin oxide, is available from a variety of sources at a reasonable price (e.g., from Pilkington (Toledo, Ohio) as TEC 15, TEC 8). These and other conductors such as ITO and others are also available in large sizes due to the demands faced by flat panel display and solar cell industry on large coated substrates. For mirrors one may also use metal coatings on substrates as one of the conductive electrode layers. Particularly electrochromic rear-view mirrors for vehicles and windows for aircrafts and vehicles which are bent could be produced by laminating an electrolyte sheet between two appropriately bent substrates. It will be desirable to make solid EC devices using the lamination process without having to further coat the conductive substrates with any additional electrode layers.